Selecting spreading code in spread spectrum system

A communication system using a code division multiple access method, comprising:

• a base transceiver station and terminal equipment communicating with the base transceiver station;
• means for maintaining a code tree which includes a hierarchically branching structure where a spreading code on a higher level of the code tree is related to two spreading codes on a lower level, symbols of the first half of the spreading codes on the lower level being congruent with those of the spreading code on the higher level;
• and
• means for selecting a spreading code from the code tree for the use of the terminal equipment for transmission from the base transceiver station to the terminal equipment,
• wherein the means for selecting a spreading code are configured to:
• search the code tree for a highest level which includes at least one branch of the code tree, spreading codes in subordinate relation to the branch being allocatable, and
• allocate a spreading code related to the branch of the sought level for the use of the terminal equipment.

A base transceiver station in a CDMA mobile telephone system, comprising:

• means for maintaining a code tree which determines spreading codes to be used in the system, in which code tree spreading codes according to a certain spreading factor are located on the same level, the levels being arranged such that the level of the lowest spreading factor is located highest in the tree and the rest of the levels are located below the highest level in an order according to the spreading factor, from the lowest to the highest;
• means for selecting a spreading code from the code tree for the communication between the base transceiver station and terminal equipment communicating with the base transceiver station,
• wherein the means for selecting a spreading code are configured to:
• select a highest level in the code tree which includes at least one branch of the code tree whose spreading codes are allocatable, and
• allocate for use a spreading code generated from a branch of the selected level whose spreading codes are allocatable.